Hydrology of Polk County, Florida - USGS · Hydrology of Polk County, Florida By Rick M. Spechler and Sharon E. Kroening Prepared in cooperation with the Polk County Board of County

Hydrology of Polk County, Florida

By Rick M. Spechler and Sharon E. Kroening

Prepared in cooperation with the Polk County Board of County Commissioners South Florida Water Management District Southwest Florida Water Management District St. Johns River Water Management District

Scientific Investigations Report 2006-5320

U.S. Department of the Interior U.S. Geological Survey

U.S. Department of the InteriorDIRK KEMPTHORNE, Secretary

U.S. Geological SurveyMark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:Spechler, R.M., and Kroening, S.E., 2007, Hydrology of Polk County, Florida: U.S. Geological Survey Scientific Investigations Report 2006-5320, 114 p.

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Contents

Abstract ...........................................................................................................................................................1Introduction ....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2Previous Investigations........................................................................................................................3Acknowledgments ................................................................................................................................3Site-Numbering System .......................................................................................................................3

Description of Study Area ............................................................................................................................4Population, Industry, and Land Use ...................................................................................................5Physiography .........................................................................................................................................6Climate ....................................................................................................................................................8Ground-Water Use ..............................................................................................................................10

Chapter 1—Ground-Water Resources of Polk County ................................................................13Data Collection .............................................................................................................................................13Geologic Framework ...................................................................................................................................13

Stratigraphy .........................................................................................................................................13Karst Features .....................................................................................................................................18

Ground-Water Resources ..........................................................................................................................18Surficial Aquifer System ....................................................................................................................19Intermediate Confining Unit and Intermediate Aquifer System ..................................................26Floridan Aquifer System.....................................................................................................................33

Upper Floridan Aquifer ..............................................................................................................33Middle Semiconfining Unit and Middle Confining Unit .......................................................35Lower Floridan Aquifer .............................................................................................................37Sub-Floridan Confining Unit .....................................................................................................38Ground-Water Flow System .....................................................................................................38

Recharge and Discharge .................................................................................................38Potentiometric Surface ....................................................................................................38

Long-Term Trends in Ground-Water Levels ....................................................................................42Head Relations ....................................................................................................................................46Water Budget ......................................................................................................................................50

Ground-Water Quality .................................................................................................................................51Surficial Aquifer System ....................................................................................................................52Intermediate Aquifer System ............................................................................................................57Floridan Aquifer System.....................................................................................................................58

Vertical Distribution of Chloride and Sulfate Concentrations ............................................62Chapter 2—Streamflow and Lake-Level Characteristics in Polk County ............................67Purpose and Scope .....................................................................................................................................67Methods.........................................................................................................................................................67Streamflow and Lake-Level Characteristics ...........................................................................................67

Streamflow Characteristics ..............................................................................................................68Peace River Basin .....................................................................................................................70Kissimmee River Basin .............................................................................................................74Alafia, Hillsborough, Ocklawaha, and Withlacoochee River Basins ................................77

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Low-Flow and Flood-Frequency Statistics .....................................................................................77Lake Characteristics...........................................................................................................................77

Regulation of Lake Levels .........................................................................................................81Temporal Trends in Lake Levels ..............................................................................................84Factors Controlling Lake Levels ..............................................................................................85

Summary........................................................................................................................................................88Selected References ...................................................................................................................................91

Appendix 1. Well and spring data-collection sites ......................................................................... 99-105Appendix 2. Chemical and physical data for water from the surficial aquifer system,

intermediate aquifer system, and the Upper Floridan aquifer wells in Polk and parts of adjacent Highlands, Hillsborough, Lake, Orange, and Osceola Counties .... 107-112

Appendix 3. Lake and stream data-collection sites ..................................................................... 113-114

Figures

1. Map showing location of study area in central Florida..........................................................4 2. Graph showing historical population for Polk County ............................................................5 3-4. Maps showing generalized: 3. Land use in Polk County, 1995 ..........................................................................................6 4. Physiography of Polk County ............................................................................................7 5-6. Graphs showing: 5. Annual rainfall at Lakeland, Mountain Lake, and Avon Park, Florida,

1931-2003 ..............................................................................................................................9 6. Monthly evapotranspiration at the Disney Wilderness Preserve in eastern

Polk County, August 2000 to December 2005 ...............................................................10 7. Diagram showing total ground-water use, by category, for 2000 ......................................11 8. Piechart showing historical total ground-water use in Polk County, 1965-2002 ..............11 9-10. Maps showing location of: 9. Wells with periodic or continuous water-level data ..................................................14 10. Wells and spring where water-quality data were collected from 1998-2003 .........15 11. Lithologic chart showing relation of stratigraphic and hydrogeologic units ...................16 12. Geologic map of Polk County ....................................................................................................17 13. Aerial photograph showing sinkhole-formed lakes near Winter Haven, Florida ............19 14. Map showing location of sinkholes and depressions in Polk County ...............................20 15. Photograph showing loss of water from the Peace River through underlying

conduit during low-flow period, May 2004 .............................................................................21 16. Map showing location of hydrogeologic sections ................................................................22 17-18. Diagrams showing generalized hydrogeologic sections: 17. A-A’ and B-B’.....................................................................................................................23 18. C-C’ and D-D’ .....................................................................................................................24 19. Map showing generalized thickness of the surficial aquifer system ................................25 20. Graphs showing water levels at selected wells tapping the surficial aquifer system .....26

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21-25. Maps showing: 21. Transmissivity of the surficial and intermediate aquifer systems ............................27 22. Generalized altitude of the top of the intermediate confining unit and the

intermediate aquifer system ...........................................................................................28 23. Generalized thickness of the intermediate confining unit and the

intermediate aquifer system ...........................................................................................29 24. Water levels of the intermediate aquifer system (Zone 2), September 2003 .........30 25. Water levels of the intermediate aquifer system (Zone 2), May 2004 .....................31 26. Graphs showing water levels at selected wells tapping the intermediate

aquifer system ............................................................................................................................3227-31. Maps showing: 27. Altitude of the top of the Floridan aquifer system .......................................................34 28. Transmissivity of the Upper Floridan aquifer ...............................................................36 29. Altitude of the top of the middle confining unit ...........................................................37 30. Potentiometric surface of the Upper Floridan aquifer, September 2003 .................39 31. Potentiometric surface of the Upper Floridan aquifer, May 2004 ............................40 32. Graphs showing water levels in selected wells tapping the Upper Floridan aquifer .......4133-34. Maps showing: 33. Predevelopment potentiometric surface of the Upper Floridan aquifer .................42 34. Change in the potentiometric surface of the Upper Floridan aquifer from

predevelopment to average 2000-2004 conditions .....................................................4335-37. Graphs showing: 35. Discharge at Kissengen Spring, 1898-1960 ..................................................................43 36. Long-term water levels in observation wells tapping the surficial aquifer

system and the Upper Floridan aquifer.........................................................................45 37. Water levels in selected wells open to the surficial aquifer system, the

intermediate aquifer system, and the Upper Floridan aquifer ..................................47 38. Map showing head differences between the surficial aquifer system and the

Upper Floridan aquifer, May 2004 ............................................................................................48 39. Graphs showing water levels during drilling of monitoring wells ......................................49 40. Diagram showing water budget for Polk County, Florida, 1994-2003 .................................50 41. Trilinear diagram for water from wells tapping the surficial aquifer system ...................5242-45. Maps showing generalized distribution of: 42. Specific conductance in water from the surficial aquifer system ...........................53 43. Chloride concentrations in water from the surficial aquifer system .......................54 44. Sulfate concentrations in water from the surficial aquifer system .........................55 45. Nitrate concentrations in water from the surficial aquifer system .........................56 46. Trilinear diagram for water from wells tapping the intermediate aquifer system ...........57 47. Map showing generalized distribution of selected constituents in water from

the intermediate aquifer system ..............................................................................................58 48. Trilinear diagram for water from wells tapping the Upper Floridan aquifer .....................5949-53. Maps showing generalized distribution of: 49. Specific conductance in water from the Upper Floridan aquifer ............................60 50. Chloride concentrations in water from the Upper Floridan aquifer .........................61 51. Sulfate concentrations in water from the Upper Floridan aquifer ...........................62 52. Hardness concentrations in water from the Upper Floridan aquifer ......................63 53. Nitrate concentrations in water from the Upper Floridan aquifer ...........................64

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54. Graphs showing chloride and sulfate concentrations in water samples obtained during drilling of monitoring wells ...........................................................................................65

55-57. Maps showing: 55. Estimated altitude of water in the Floridan aquifer system having chloride

concentrations greater than 250 milligrams per liter .................................................66 56. Location of lakes and streams analyzed in this report ..............................................68 57. Major surface-water drainage basins, tributaries, and lakes ..................................69 58. Flow-duration hydrographs for Peace River at Bartow, water years 1979-2003 .............70 59. Graph showing flow-duration curves for selected stream sites in Polk County,

water years 1979-2003 ...............................................................................................................71 60. Graph showing flow-duration curves for Kissimmee River at S-65, water years

1930-1969 and water years 1979-2003 ......................................................................................75 61. Flow-duration hydrographs for Kissimmee River at S-65 (site 74), water years

1930-1969 and 1979-2003 ............................................................................................................76 62. Map showing location of Lake Hamilton and Winter Haven Chain of Lakes ....................82 63-65. Graphs showing: 63. Generalized seasonal variations in lake levels in Lake Deeson, 1954-2003 ...........83 64. Seasonal variations in lake levels in Saddle Blanket Lake during a period of

below normal rainfall........................................................................................................83 65. Seasonal variations in lake levels and the minimum daily air temperatures

at a lake (Swim Lake) affected by ground-water pumpage ......................................84 66-67. Maps showing temporal trends in lake levels in: 66. Polk County, 1960-2003 ....................................................................................................86 67. Polk County, 1990-2003 ....................................................................................................87

Tables 1. Results of trend analysis for long-term observation wells and for rainfall stations ...............44 2. Mean annual flow and runoff for selected streams in Polk County, water years

1991-2003 .............................................................................................................................................69 3. Temporal trends in streamflow over 20-year periods for Peace River at Bartow ..................72 4. Temporal trends in streamflow over 30-year periods for Peace River at Bartow ..................72 5. Temporal trends in streamflow over 40-, 50-, and 60-year periods for Peace River

at Bartow ............................................................................................................................................73 6. Low-flow frequency statistics for Catfish Creek near Lake Wales ...........................................78 7. Low-flow frequency statistics for Fox Branch near Socrum .....................................................78 8. Low-flow frequency statistics for Green Swamp Run near Eva ................................................78 9. Low-flow frequency statistics for Bowlegs Creek near Fort Meade ........................................79 10. Low-flow frequency statistics for Livingston Creek near Frostproof .......................................79 11. Low-flow frequency statistics for Peace Creek Drainage Canal near Wahneta ...................79 12. Low-flow frequency statistics for Tiger Creek near Babson Park ............................................80 13. Low-flow frequency statistics for Peace River at Bartow .........................................................80 14. Low-flow frequency statistics for Peace River at Fort Meade ..................................................80 15. Flood-flow frequency statistics for selected sites in Polk County ............................................81 16. Temporal trends in mean annual water levels for selected lakes in Polk County,

1960-2003 .............................................................................................................................................85

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Conversion Factors, Vertical Datum, Abbreviations, and Acronyms

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

Transmissivity*

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d)

Leakance

foot per day per foot [(ft/d)/ft] 1 meter per day per meter

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C = (°F – 32) / 1.8

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29).

Altitude, as used in this report, refers to distance above the vertical datum.

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot squared per day (ft2/d), is used for convenience.

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Acronyms and Additional Abbreviations

AMO Atlantic Multidecadal Oscillation

CaCO3 calcium carbonate

ET evapotranspiration

FGS Florida Geological Survey

LOWESS locally weighted scatterplot

µg/L micrograms per liter

µS/cm microsiemens per centimeter at 25 °C

mg/L milligrams per liter

NOAA National Oceanic and Atmospheric Administration

NWIS National Water Data Information System

NO3- nitrate

NO2- nitrite

N nitrogen

PDO Pacific Decadal Oscillation

ROMP Regional Observation and Monitoring-Well Program

SJRWMD St. Johns River Water Management District

SFWMD South Florida Water Management District

SWUCA Southern Water Use Caution Area

SWFWMD Southwest Florida Water Management District

QS spring discharge

QO subsurface outflow

QR surface-water runoff

USGS U.S. Geological Survey

viii

aquifer system. The Floridan aquifer system, a thick sequence of permeable limestone and dolostone, consists of the Upper Floridan aquifer, a middle semiconfining unit, a middle confining unit, and the Lower Floridan aquifer. The Upper Floridan aquifer provides most of the water required to meet demand in Polk County.

Data from about 300 geophysical and geologic logs were used to construct hydrogeologic maps showing the tops and thicknesses of the aquifers and confining units within Polk County. Thickness of the surficial aquifer system ranges from several feet thick or less in the extreme northwestern part of the county and along parts of the Peace River south of Bartow to more than 200 feet along the southern part of the Lake Wales Ridge in eastern Polk County. Thickness of the interme-diate aquifer system/intermediate confining unit is highly vari-able throughout the county because of past erosional processes and sinkhole formation. Thickness of the unit ranges from less than 25 feet in the extreme northwestern part of the county to more than 300 feet in southwestern Polk County. The altitude of the top of the Upper Floridan aquifer in the county ranges from about 50 feet above National Geodetic Vertical Datum of 1929 (NGVD 29) in the northwestern part to more than 250 feet below NGVD 29 in the southern part.

Water levels in the Upper Floridan aquifer fluctuate seasonally, increasing during the wet season (June through September) and decreasing during the rest of the year. Water levels in the Upper Floridan aquifer also can change from year to year, depending on such factors as pumpage and climatic variations. In the southwestern part of the county, fluctuations in water use related to phosphate mining have had a major impact on ground-water levels. Hydrographs of selected wells in southwestern Polk County show a general decline in water levels that ended in the mid-1970s. This water-level decline coincides with an increase in water use associated with

AbstractLocal water managers usually rely on information

produced at the State and regional scale to make water-resource management decisions. Current assessments of hydrologic and water-quality conditions in Polk County, Florida, commonly end at the boundaries of two water management districts (South Florida Water Management District and the Southwest Florida Water Management District), which makes it difficult for managers to determine conditions throughout the county. The last comprehensive water-resources assessment of Polk County was published almost 40 years ago. To address the need for current county-wide information, the U.S. Geological Survey began a 3 ½-year study in 2002 to update information about hydrologic and water-quality conditions in Polk County and identify changes that have occurred.

Ground-water use in Polk County has decreased substan-tially since 1965. In 1965, total ground-water withdrawals in the county were about 350 million gallons per day. In 2002, withdrawals totaled about 285 million gallons per day, of which nearly 95 percent was from the Floridan aquifer system. Water-conservation practices mainly related to the phosphate-mining industry as well as the decrease in the number of mines in operation in Polk County have reduced total water use by about 65 million gallons per day since 1965.

Polk County is underlain by three principal hydrogeo-logic units. The uppermost water-bearing unit is the surficial aquifer system, which is unconfined and composed primarily of clastic deposits. The surficial aquifer system is underlain by the intermediate confining unit, which grades into the intermediate aquifer system and consists of up to two water-bearing zones composed of interbedded clastic and carbonate rocks. The lowermost hydrogeologic unit is the Floridan

Hydrology of Polk County, Florida

By Rick M. Spechler and Sharon E. Kroening

� Hydrology of Polk County, Florida

phosphate mining. A substantial increase in water levels that began in the mid-1970s coincides with a period of decreasing water use in the county.

Despite reductions in water use since 1970, however, over the long term, the increase in pumping in and near Polk County has resulted in a decline of the potentiometric surface of the Upper Floridan aquifer across much of the county since predevelopment times. Based on the difference between the estimated predevelopment potentiometric-surface map and water levels in wells measured in May and September and averaged from 2000 to 2004, water-level declines range from zero in the northwestern part of the county to as much as 40 feet in the southwestern part.

Water samples collected from 130 wells were used to characterize ground-water quality in Polk County. Samples from 53 wells and 1 spring in Polk and adjacent counties were collected for this project by the U.S. Geological Survey and analyzed for common inorganic constituents and nutrients. Concentrations of total dissolved solids, sulfate, and chloride in water samples from the surficial and intermediate aquifer systems generally were below State and Federal drinking-water standards. Nitrate concentrations, however, were as high as 26 milligrams per liter (mg/L) in samples from the surficial aquifer system along the Lake Wales Ridge. The application of fertilizers related to citrus farming is a likely source of nitrate to the ground water in this area.

Inorganic constituent concentrations in water from the Floridan aquifer system generally were below State and Federal drinking-water standards. Water from the Upper Floridan aquifer in most of Polk County is hard (hardness ranging from 70 to 290 mg/L), and has a dissolved-solids concentration of less than 500 mg/L. Chloride concentrations in water from the Upper Floridan aquifer range from 4.2 to 61 mg/L, and sulfate concentrations range from about 0.2 to 44 mg/L. In contrast to results from the surficial aquifer system, nitrate concentrations in the Upper Floridan aquifer generally were low (less than 0.02 mg/L) and exceeded 1.0 mg/L in only three wells.

Temporal trends in streamflow in the Peace River were updated in this study using data through 2003. The analyses also were expanded by analyzing trends over a wide range of the hydrologic regime and over several multidecadal periods. Results indicate that annual minimum to 70th percentile streamflows in the Upper Peace River began to decline in the 1950s, and this decline has persisted to 2003. Results also showed a statistically significant decrease in annual minimum streamflows in the Peace River at Bartow from 1974-1993. This decrease may be due to elimination of wastewater discharges to the stream during the mid-1980s.

Temporal trends in lake levels were analyzed to describe long-term trends (1960-2003) and trends of a shorter duration (1990-2003). About 90 percent of the lakes had no change in water levels from 1990-2003. Five of the lakes had an increas-ing trend in water levels. The increase in water levels likely is not due to increased rainfall. Annual totals at nearby rainfall stations had no significant trends during this period.

IntroductionIncreasing demands are being made on the water

resources of Polk County, Florida, as a result of rapidly increasing population and a strong agricultural industry. Changes in ground-water levels or water quality that may have resulted from the redistribution of pumping stresses, however, have not been documented on a countywide basis. The last comprehensive hydrogeologic investigation of Polk County was completed in 1966. The U.S. Geological Survey (USGS) and other State and local agencies continue to collect informa-tion on the surface-water and ground-water resources of Polk County. Current assessments of hydrologic and water-quality conditions conducted by these agencies commonly end at the water management district boundaries, which makes it difficult for water-resource managers to determine hydrologic and water-quality conditions throughout the county. Three of Florida’s water management districts (St. Johns River, South Florida, and Southwest Florida Water Management Districts) have had jurisdiction over parts of the county. An analysis of long-term and current hydrologic data will enable water-resource managers to better evaluate changes in hydrologic conditions. Updated information can be used to redefine base-line conditions against which future changes can be quantified. To address the need for current countywide information, the USGS, in cooperation with Polk County, the South Florida Water Management District (SFWMD), the St. Johns River Water Management District (SJRWMD), and the Southwest Florida Water Management District (SWFWMD) conducted a 3 ½-year study from 2002 to 2006 to evaluate the hydrogeol-ogy and ground-water quality of Polk County and to provide an updated evaluation of surface water including streamflow and lake-level trends and characteristics. The results of the study are summarized in this report.

Purpose and Scope

This report presents the results of a study to describe and update information on the hydrogeology of the surficial, inter-mediate, and Floridan aquifer systems in Polk County, Florida, characterize water-quality conditions in the three aquifers, and assess long-term trends in the ground-water and surface-water resources. Chapter 1 of the report describes: (1) the lithology, depth, thickness, and extent of the surficial aquifer system, intermediate aquifer system, intermediate confining unit, and the Floridan aquifer system in Polk County; (2) water levels and water-level changes in the aquifer systems; and (3) the water-quality characteristics of the surficial, intermediate and Floridan aquifer systems. Chapter 2 describes trends in lake stage and streamflow by updating flow and lake stage data and duration curves.

Information presented in the report was compiled from data collected during this investigation by the USGS, SWFWMD, SFWMD, and SJRWMD. Additional informa-tion also was obtained from published reports by the USGS,

SFWMD, Florida Geological Survey (FGS), and private consultants, and from unpublished data by the USGS and FGS. New data collected during this investigation included water-quality samples, ground-water level measurements, and lithologic logs.

Previous Investigations

Numerous reports have described the hydrology, geology, and ground-water resources of Polk County. Discussions of Florida geology with reference to Polk County are included in reports by Cooke (1945) and Stringfield (1966). Miller (1986) describes the hydrogeologic framework of the Floridan aquifer system.

The first comprehensive investigation on the hydrogeol-ogy and ground-water resources of Polk County was done by Stewart (1966). A number of studies have described the hydro-geology of selected areas within Polk County. Shaw and Trost (1984) evaluated the regional hydrogeology of the Kissimmee River Basin. Duerr and others (1988) and Knochenmus (2006) described the hydrogeologic framework of the intermediate aquifer system in west-central Florida. O’Reilly and others (2002) described the hydrogeology and water quality of the Lower Floridan aquifer in east-central Florida, which included part of Polk County. Pride and others (1966), Grubb (1978), and Grubb and Rutledge (1979) described the hydrology of the Green Swamp area. Robertson (1971; 1973) discussed the hydrology of the Lakeland Ridge. The hydrogeology of the Lake Wales Ridge was described in several reports, includ-ing Barcelo and others (1990) and Yobbi (1996). Hutchinson (1978) described the surficial and intermediate aquifer systems of the upper Peace River and eastern Alafia River Basins. Kaufman (1967) and Robertson and Mills (1974) described the effects of ground-water pumping in the Peace and Alafia River Basins. Basso (2003) discussed the surface-water/ground-water relation in the Upper Peace River Basin. Lewelling and others (1998) assessed the hydraulic connection between ground water and the Peace River.

Several reports evaluated the ground-water quality in Polk County. Swancar and Hutchinson (1995) discussed the chemical and isotopic composition and potential for contami-nation of water in the Upper Floridan aquifer in west-central Florida. Stewart (1966) presented a general reconnaissance of ground-water quality in Polk County. Barr (1992) evaluated the potential for ground-water contamination of the surficial, intermediate, and Floridan aquifer systems in Polk County. Miller and Sutcliffe (1982), Rutledge (1987), and Lewelling and Wylie (1993) described the quality of water in the surficial aquifer system in parts of the phosphate region of south-western Polk County. Moore and others (1986) summarized information from the ambient ground-water quality monitoring program for the SWFWMD. Nitrate in shallow ground water in the vicinity of the Lake Wales Ridge was evaluated by Tihansky and Sacks (1997). Pesticides and nitrate concentra-tions in the surficial aquifer system underlying citrus areas in

the northern part of the Lake Wales Ridge were evaluated in a land-use comparison study (German, 1996). Agricultural chemicals in the surficial aquifer system in the Lake Wales Ridge were investigated by Choquette and others (2005).

Several investigators have employed continuous high-resolution seismic-reflection techniques in Polk County lakes and rivers to describe geologic structure at depth—including Evans and others (1994), Tihansky and others (1996), and Lewelling and others (1998).

Ground-water flow modeling studies that include all or part of the study area are presented by Grubb and Rutledge (1979), Wilson and Gerhart (1982), Ryder (1982; 1985), Tibbals (1990), Barcelo and Basso (1993), Yobbi (1996), and Sepúlveda (2002).

Several hydrologic assessments have focused on lakes that lie within Polk County. The hydrology and limnology of Crooked Lake were described by Bradbury and others (1978). Sacks and others (1998) estimated ground-water exchange with lakes in the ridge areas of Polk and Highlands Counties by using water-budget and chemical mass-balance approaches. Swancar and others (2000) estimated ground-water exchange at Lake Starr.

Acknowledgments

The authors gratefully acknowledge the assistance given by many organizations and individuals during the study and especially appreciate the cooperation received from Chris Sweazy, Emily Hopkins Richardson, and Cynthia Gefvert of the South Florida Water Management District; Jeff Spence of the Polk County Board of County Commissioners; Margit Crowell, Eric DeHaven, and Joseph Haber of the Southwest Florida Water Management District; and Nolan Col of the St. Johns River Water Management District. Appreciation also is expressed to the residents and private companies in the area who permitted access to their properties and allowed the sampling of water and measuring of water levels in their wells.

Site-Numbering System

The USGS assigns a unique site identification number to each inventoried well and surface-water site. A 15-digit number based on latitude and longitude is used to identify wells in the USGS National Water Data Information System (NWIS). The first six digits denote the degrees, minutes, and seconds of latitude; the next seven digits denote degrees, minutes, and seconds of longitude; and the last two digits denote a sequential number for a site within a one-second grid. For example, well 280253081235801 is the first well inventoried at latitude 28˚02’53” N, longitude 081˚23’58” W. The latitude and longitude stored in NWIS, however, should be used rather than those defined by the 15-digit site number because the initial measurements may be inaccurate or succes-sive measurements more accurate. Surface-water sites that are

Introduction �


part of the long-term data-collection network are assigned an eight-digit downstream order number, such as 02294650 for the Peace River at Bartow, which designates the major river basin (02) and the order in which the tributary joins the main stream. Surface-water sites that are not part of the long-term network usually are given a 15-digit number.

Description of Study AreaPolk County, located in the central part of the Florida

peninsula, is Florida’s fourth largest county (fig. 1). It is bordered on the north by Lake and Sumter Counties, on the east by Osceola County, on the south by Hardee and Highlands Counties, and on the west by Hillsborough and Pasco Counties. Polk County is approximately 40 miles wide and 50 miles long and has a surface area of about 1,823

square miles (mi2), of which 187 mi2 are water (Purdum and others, 1988). Land-surface elevations range from about 50 to 305 feet (ft) above NGVD 29 (Stewart, 1966); however, most of the land lies between 75 and 250 ft above NGVD 29 (Heath, 1961; Southwest Florida Water Management District, 1988). The lowest elevations are found in the eastern part of the county, and the highest elevations are found on the Lake Wales Ridge in the vicinity of the city of Lake Wales and Babson Park (Stewart, 1966). The western part of Polk County is included within the SWFWMD, and the eastern part is included within the SFWMD (fig. 1). A small area in the northern part of the county that corresponded to the Ocklawaha River basin was once part of the SJRWMD, but in 2003 boundary lines were redrawn and this area is now under the jurisdiction of the SWFWMD. All of Polk County that falls under the jurisdiction of the SWFWMD is part of the Southern Water Use Caution Area (SWUCA), which

GREENSWAMP

LakeWeohyakapka

LakeRosalie

CrookedLake

LakeHancock

WithlacoocheRi

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Ri

er

Kissimm

ever

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SaddleCreek

Saddle

Creek

LakeHatchineha

LakePierce

LakeMarion

POLK COUNTY

LAKECOUNTY

SUM

TER

COUN

TY

HILL

SBOR

OUGH

COU

NTY

PASC

O CO

UNTY

HARDEE COUNTY HIGHLANDS COUNTYMANATEECOUNTY

OSCEOLACOUNTY

ORANGECOUNTY

SJRWMD

SWFW

MDSFW

MD

SFWMD

SWFW

MD81°15′30′45′82°00′

28°15′

28°00′

27°45′

Base modified from U.S. Geological Survey digital data, 1:100,000, 1985Universal Transverse Mercator projection, zone 17 0 10 MILES

0 10

5

5 15 KILOMETERS

STUDY AREA

Lakeland

Polk City

Davenport

Dundee

Lake WalesBartow

BradleyJunction

Fort Meade Frostproof

WinterHaven

Auburndale

LakeAlfred

EagleLake

HighlandPark

HillcrestHeights

LakeHamilton

HainesCity

Mulberry

MountainLake

Avon Park

Lake LouisaState Park

BabsonPark

17

I-4

17

98

17

27

27

98

92

98

60

60

6060

630

KissengenSpring

DisneyWildernessPreserve

Figure 1. Location of study area in central Florida.

includes all or part of eight counties in southwestern Florida. This water-use caution area was designated in 1992, when it was recognized that increasing ground-water withdrawals (in response to increasing growth) resulted in declines in aquifer heads causing saltwater intrusion in coastal areas, lowered lake levels in the upland areas, and reduced baseflow in some river reaches.

Population, Industry, and Land Use

Since the 1960s, there has been a rapid increase in population and this trend is expected to continue. From 1960 to 2004, the population of Polk County increased from about 195,000 to 528,000 (fig. 2). The population of Polk County is projected to reach about 676,000 by 2020. In 2004, the county was the 10th largest in terms of population in the State (Office of Economic and Demographic Research, 2005). Polk County has 17 municipalities (fig. 1). The largest in popula-tion is Lakeland and the second largest is Winter Haven. Other municipalities include Auburndale, Bartow, Davenport, Dundee, Eagle Lake, Fort Meade, Frostproof, Haines City, Highland Park, Hillcrest Heights, Lake Alfred, Lake Hamilton, Lake Wales, Mulberry, and Polk City.

Polk County is one of the leading counties in industrial development in the State, having about 450 manufacturing companies and 3,114 farms in 2002 (U.S. Department of Agriculture, 2005). It ranks first in phosphate production (Polk County Department of Economic Development, 2005) and

second in cattle production (U.S. Department of Agriculture, 2005). The county also ranks first in the State in citrus produc-tion for 2003-2004, producing nearly 14 percent of Florida’s citrus (U.S. Department of Agriculture, 2005).

Agriculture, wetlands, urban land, forests, and mining were the major land-use categories in the county in 1995 (fig. 3). Agricultural land use composed about 40 percent of the county, in which citrus is the primary agricultural product. Agricultural lands are scattered throughout the county, but are concentrated along the ridges. Wetlands composed about 30 percent of the county and generally are found in the Green Swamp area of northern Polk County and east of the Lake Wales Ridge. Urban land composed about 12 percent of the county, and is mostly concentrated around the cities of Lakeland, Bartow, Auburndale, Winter Haven, and Lake Wales. Forest covered about 6 percent of the county, primarily in the eastern one-third of the county. Mining areas composed about 4 percent of the county, and are found primarily in the southwestern part. Phosphate and, to a lesser degree, sand mining are the primary types of mining operations.

A comparison of the extent of urban land use between 1977 and 1995 indicates that the amount of urban area increased from about 10 to 12 percent. Most of the increase in urbanization occurred in an east-west band across the central part of the county, which included the cities of Lakeland, Auburndale, Winter Haven, and Lake Wales. The eastern part of the county (east of the Lake Wales Ridge) has had relatively little increase in urbanization.

1960 1970 1980 1990 2000 2010 2020YEAR

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

POPU

LATI

ON

Figure �. Historical population for Polk County (from the Office of Economic and Demographic Research, 2005).

Description of Study Area �


Physiography

Polk County is divided into 10 physiographic provinces (White, 1970): the Polk Upland, Lake Upland, Winter Haven Ridge, Lake Henry Ridge, Lakeland Ridge, Lake Wales Ridge, Bombing Range Ridge, Osceola Plain, Western Valley, and Intra Ridge Valley (fig. 4). In general, these physiographic prov-inces are four basic types: uplands, ridges, valleys, and plains.

Much of the western part of Polk County lies in the Polk and Lake Uplands. These uplands are characterized by moder-ate relief, shallow lakes, and moderate water-table depths. The Polk Upland is a broad sandy area that ranges in altitude from about 65 ft above NGVD 29 along parts of the Peace River to about 150 ft above NGVD 29. In the northern part

of the county, the Polk Upland merges with the Lake Upland. The boundary between the Polk and Lake Uplands is inferred because there is not a distinct topographic break between the two uplands (White, 1970). The part of the Lake Upland that is in Polk County ranges in altitude from 100 to 135 ft above NGVD 29. In much of the Lake Upland lies the Green Swamp. The Green Swamp is a composite of many swamps that are distributed fairly uniformly over the area. Interspersed among the swamps are low ridges, hills, and flatlands. In the extreme northwestern part of the county lies the Western Valley physio-graphic province. The Western Valley is a low, irregular valley produced by the erosion of soluble sediments (Campbell, 1986). Elevations of the Western Valley that lie within Polk County range from 75 to about 120 ft above NGVD 29.

Figure �. Generalized land use in Polk County, 1995.

Three north-northwest to south-southeast trending ridges rise from the surface of the Polk Upland. These ridges have the highest land-surface elevations in the county and are character-ized by closed basin lakes and sinkholes, deep water tables, and subsurface drainage. Surface drainage features generally are absent. The easternmost ridge within the Polk Upland (the Winter Haven Ridge) consists mostly of small ridge remnants, reaching altitudes of about 200 ft above NGVD 29. The southern extension of the Winter Haven Ridge is referred to as the Lake Henry Ridge. Maximum altitudes along this ridge are 230 ft above NGVD 29. The westernmost ridge, the Lakeland Ridge, begins about 10 miles north of Lakeland and extends to the south of Bartow, reaching altitudes of about 270 ft above NGVD 29.

The most prominent ridge in Polk County is the Lake Wales Ridge (fig. 4). The Lake Wales Ridge, located east of the Winter Haven Ridge, borders the eastern edge of the Polk Upland and extends southward from Lake County, through Polk County and into Highlands County. The Lake Wales Ridge is the highest and longest of the ridges, with maximum altitudes of 305 ft above NGVD 29. This long, narrow, sandy ridge contains numerous sinkhole lakes and depressions, many of which do not have any surface-water outlets. In the southern part of the county, the Lake Wales Ridge is divided into two secondary ridges by the Intra Ridge Valley. This valley was formed by the dissolution of the underlying limestone and contains numerous karst features.

LAKE UPLAND

WES

TERN

VALL

EY

WINTER

HAVEN

RIDGE LAKEW

ALESRIDGE

POLK UPLAND

LAKELANDRIDGE

BOMBING

RANGE

RIDGE

OSCEOLAPLAINLAKE

HENRY

RIDGE

INTRA RIDGEVALLEY

81°15′30′45′82°00′

28°15′

28°00′

27°45′


0 10

5

5 15 KILOMETERS

Figure �. Generalized physiography of Polk County (from White, 1970).



The Osceola Plain is a broad marine terrace that lies east of the Lake Wales Ridge. It is characterized by large lakes, little relief, and altitudes that range from about 50 to 75 ft above NGVD 29. Water levels in the surficial aquifer system are at, or only a few feet below, land surface in much of the plain. In southeastern Polk County, the Bombing Range Ridge rises above the level of the Osceola Plain. Reaching altitudes of about 135 ft above NGVD 29 in Polk County, this ridge is probably the result of a former marine sand bar (White, 1970).

Climate

The climate of Polk County is classified as humid subtropical and is characterized by hot, wet summers and mild, relatively dry winters. The mean annual temperature at Lakeland is 73 ˚F, and the mean monthly temperature ranges from a low of about 61 ˚F in January to 83 ˚F in August. Temperatures commonly exceed 90 ˚F from June to September, and may fall below freezing for a few days in the winter months.

Rainfall is unevenly distributed throughout the year. About 55 percent of the annual rainfall total is derived from thunderstorms that occur frequently during the months of June through September. During the summer, thunderstorms can produce heavy but localized rainfall, resulting in several inches of precipitation falling in one location and little or none falling a few miles away. During the summer months and early fall, occasional tropical storms and hurricanes also can bring heavy precipitation into the area. During the winter, rainfall is associated with frontal system activity, which is usually of a longer duration and areally more uniform than summer convectional precipitation. April and November typically are the driest months.

The National Oceanic and Atmospheric Administration (NOAA) records indicate that long-term average annual rain-fall totals are similar throughout the county. Rainfall data for a 73-year period from 1931 to 2003 at the Lakeland, Mountain Lake, and Avon Park (Highlands County) stations are shown in figure 5. The mean annual rainfall was about 51 inches (in.) at the Lakeland and Mountain Lake stations and about 53 in. at the Avon Park station.

Drought conditions prevailed throughout much of Florida during 2000. The lowest annual rainfall totals recorded at the Avon Park and Mountain Lake stations occurred in 2000: 26.10 and 29.53 in., respectively. At the Lakeland site, however, the lowest annual rainfall total was 35.83 in. measured in 1961. Annual rainfall totals of more than 74 in. were measured at both the Avon Park and Mountain Lake stations in 1953, and an annual rainfall total of 70.24 in. was measured at Lakeland in 1959.

A considerable amount of variation in annual rainfall occurs from year to year, sometimes making it difficult to determine whether annual rainfall totals changed substantially

over time. Patterns are apparent at some of the rainfall stations (fig. 5). From 1931 to 1960, the average annual rainfall was 53.9 and 55.3 in. at Mountain Lake and Avon Park, respectively. At Lakeland, the average rainfall was 51.3 in. during this period. In contrast, average annual rainfall from 1961 to 2003 was lower, 48.5 and 50.9 in. at Mountain Lake and Avon Park, respectively. At Lakeland, however, the aver-age annual rainfall during this period was not much different at 50.1 in.

Several investigators (Barcelo and others, 1990; Flannery and Barcelo, 1998; Basso and Schultz, 2003) reported lower rainfall amounts in the county from 1960-2000 compared to earlier decades. These multidecadal variations in rainfall may result from alternating cycles of warmer and cooler sea-surface temperatures in the North Atlantic and Pacific Oceans. Sea-surface temperatures in the North Atlantic Ocean vary by about 0.4 °C, which is referred to as the Atlantic Multidecadal Oscillation (AMO) (Enfield and others, 2001). These variations in temperature likely are caused by natural internal variations in the strength of the ocean thermohaline circulations and the associated meridional heat transport. Warm phases of the AMO have occurred from 1930-1960 and 1995-2004, and cool phases have occurred from 1905-1925 and 1970-1990 (McCabe and others, 2004). Enfield and others (2001) have shown the AMO has a strong influence on rainfall in the conterminous United States. Warm phases of the AMO are correlated with dry conditions in most of the conterminous United States; however, in Florida it is generally correlated with wet conditions. Sea-surface temperatures in a large part of the northern Pacific Ocean also vary on multidecadal cycles, which is referred to as the Pacific Decadal Oscillation (PDO) (Mantau and others, 1997). These variations also may affect rainfall in Florida. When sea-surface temperatures along the coast of North America are unusually warm, there is a strong tendency for temperatures in the central Pacific Ocean to be anomalously cool. This is referred to as a cool phase of the PDO. Cool phases of the PDO generally are associated with below-average precipitation from March through October in the southern United States and have occurred from 1890-1924 and 1947-76 (Mantau and others, 1997).

McCabe and others (2004) decomposed the drought frequency in the Nation into the primary factors affecting variability; most of the variability was attributed to the AMO, PDO, and a factor related to increasing North American temperatures. The effect that both AMO and PDO conditions have on droughts in the Nation was analyzed by McCabe and others (2004). Under cool AMO conditions and the combination of warm AMO and cool PDO conditions, there is a tendency for above-normal drought frequency in most of Florida. McCabe and Wolock (2002) reported a change in precipitation across the eastern Unites States around 1970 that may be related to a shift in climatic conditions.

5 YEARMOVINGAVERAGE

5 YEAR MOVING AVERAGE

5 YEAR MOVINGAVERAGE

LAKELAND

MOUNTAIN LAKE

AVON PARK

0

10

20

30

40

50

60

70

80

1930 1940 1950 1960 1970 1980 1990 2000YEAR

RAIN

FALL

, IN

INCH

ES

0

0

10

20

30

40

50

60

70

80

10

20

30

40

50

60

70

80

90

Average rainfall = 50.7 inchesMinimum rainfall = 29.53 inchesMaximum rainfall = 74.91 inches



Figure �. Annual rainfall at Lakeland, Mountain Lake, and Avon Park, Florida, 1931-2003.


10 Hydrology of Polk County, Florida

Most of the rainfall returns to the atmosphere by evapotranspiration, which is defined as the evaporation of water from soil and water surfaces and transpiration of plants. About 60 percent of the annual evapotranspiration occurs from May to October (Southwest Florida Water Management District, 1988). Locally, evapotranspiration varies with the evaporative demand of the atmosphere and the availability of water. The upper limit of evapotranspiration is approxi-mately equal to the rate at which water can evaporate from a free-water surface under natural conditions (Tibbals, 1990). Evapotranspiration rates are highest in the lakes, swamps, and marshes, where water is near or above land surface much of the time. Lake evaporation rates measured at Lake Starr in Polk County for a 2-year period (August 1996 to July 1998) were 57.08 and 55.88 inches per year (in/yr), respectively (Swancar and others, 2000).

During 2001-2005, annual evapotranspiration rates ranged from 34.0 to 40.2 in/yr (D.M. Sumner, U.S. Geological Survey, written commun., 2006) at a Bahia grass/palmetto site in eastern Polk County where the water table is shallow (fig. 6). The lowest rates of evapotranspiration in Polk County occur along the ridges where the surficial sediments are permeable and the depth to the water table is greater. Tibbals (1990) estimated the relation of evapotranspiration to water-table depth and determined that the minimum rate of evapo-transpiration in east-central Florida occurred where the water table was greater than 13 ft below land surface. In a study along the Lake Wales Ridge in Orange County, Sumner (1996) determined an annual evapotranspiration rate of about 27 in. at a site with a deep water table. This rate is probably close to a minimum evapotranspiration value for central Florida.

Ground-Water Use

The Upper Floridan aquifer is the principal source of water supply in Polk County. The aquifer supplies nearly all the ground water used for commercial-industrial self-supplied, public-supply, domestic self-supplied, agricultural irrigation uses, and recreational irrigation. In 2000, about 4 percent of the total amount of ground-water withdrawn was from the surficial or intermediate aquifer systems in Polk County (Marella, 2004). At present (2005), no water is withdrawn from the Lower Floridan aquifer in Polk County. Ground-water withdrawals vary from season to season and from year to year, primarily as a function of the amount and distribution of rainfall. Of the total water withdrawn in 2000, 48 percent was used for agricultural irrigation, 23 percent for public supply, 21 percent for commercial/industrial self-supplies, 4 percent for domestic self-supplied, 3 percent for recreational irrigation, and 1 percent for thermoelectric power generation (fig. 7).

Ground-water use has decreased substantially in Polk County since 1965. In 1965, total ground-water withdrawals in Polk County were about 350 million gallons per day (Mgal/d) (fig. 8). In 2002, withdrawals totaled about 285 Mgal/d. The large declines in water use are the result of water-conservation practices related to the mining and processing of phosphate ore, as well as the decrease in the number of mines operating in Polk County. Water use from the commercial/industrial self-supplied category, which includes mining, decreased from 270 Mgal/d in 1965 to 56 Mgal/d in 2002. Some of this decline in water use, however, was partially offset by increases in water use for public supply and agriculture. From 1965 to 2002, water use for public supply increased from 26 to about 74 Mgal/d. During the same period, agricultural water use increased from 52 to 127 Mgal/d.

0

1

2

3

4

5

6

7

2000 2001 2002 2003 2004 2005

ANNUALTOTAL FOR2001 = 34.0

INCHES

ANNUALFOR

2002 =INCHES

TOTAL39.7

ANNUALFOR

2003 = 40INCHES

TOTAL.2

ANNUALFOR

2004 = 38INCHES

TOTAL.0

ANNUALFOR

2005 = 40INCHES

TOTAL.2

YEAR

MON

THLY

EVA

POTR

ANSP

IRAT

ION

,IN

INCH

ES

Figure �. Monthly evapotranspiration at the Disney Wilderness Preserve in eastern Polk County, August 2000 to December 2005 (D.M. Sumner, U.S. Geological Survey, written commun., 2006).

PUBLIC SUPPLY23%

DOMESTIC(self-supplied)

4%

COMMERCIAL /INDUSTRIAL

21(self-supplied)

%

AGRICULTURE(self-supplied)

48%

THERMOELECTRIC1%

RECREATIONAL IRRIGATION3%

POLK COUNTY331 million gallons per day

0

50

100

150

200

250

300

350

400

450

1960 1970 1980 1990 2000 2010

GROU

ND-

WAT

ER, I

N M

ILLI

ON G

ALLO

NS

PER

DAY

YEAR

TOTALGROUND-WATER

USE

PUBLIC SUPPLY

DOMESTIC SELF-SUPPLIEDCOMMERCIAL/ INDUSTRIALSELF-SUPPLIED

AGRICULTURESELF-SUPPLIED THERMOELECTRIC

RECREATIONAL IRRIGATION

TOTAL GROUND WATER

Figure �. Total ground-water use, by category, for 2000 (from Marella, 2004).

Figure �. Historical total ground-water use in Polk County, 1965-2002 (from Marella, 2004; and Southwest Florida Water Management District, 2004a, 2004b).

Description of Study Area 11

1� Hydrology of Polk County, Florida

shallow-water marine origin and are composed of limestone, dolostone, evaporite, clay, and sand that range in age from Late Cretaceous to Holocene. The major stratigraphic units of interest in Polk County, from oldest to youngest, are: the Cedar Keys Formation of late Paleocene age, the Oldsmar Formation of early Eocene age, the Avon Park Formation of middle Eocene age, the Ocala Limestone of late Eocene age, the Suwannee Limestone of early Oligocene age, the Hawthorn Group of late Oligocene to Miocene age, and the undifferentiated surficial deposits of Pliocene to Holocene ages (fig. 11). Most geologic units cropping out within Polk County (fig. 12) are composed of unconsolidated siliciclastic sediments. The exceptions, however, are in the extreme north-western part of the county and along the Peace River, where some of the sediments are composed of carbonates.

There are some differences in the geologic nomenclature used in earlier water-resource assessments of Polk County (Stewart, 1966; Pride and others, 1966) and those used in this report (fig. 11). Miller (1986) determined that the Avon Park Limestone and the Lake City Limestone could not be distinguished from each other on the basis of either lithology or fauna; therefore, all of the lithologic units within the Lake City Limestone were reclassified as Avon Park Limestone. Miller (1986) also recognized that the Avon Park Limestone contained a considerable amount of dolostone and should be called a formation (Avon Park Formation), rather than a limestone. The Ocala Group is now referred to as the Ocala Limestone, and the unit previously referred to as the Hawthorn Formation is now recognized as the Hawthorn Group (Scott, 1988). Similarly, the Tampa Member of the Arcadia Formation was formerly referred to as the Tampa Limestone or Tampa Formation.

Stratigraphy

The basal Tertiary unit within the study area is the Cedar Keys Formation of late Paleocene age (fig. 11). The Cedar Keys Formation generally has extremely low permeability, and thus, functions as the sub-Floridan confining unit at the base of the Floridan aquifer system. Conformably overly-ing the Cedar Keys Formation is the Oldsmar Limestone of Eocene age. It is composed mostly of limestone and dolostone that in places contains inclusions of gypsum and anhydrite. These evaporites were deposited in shallow, restricted marine basins on emergent areas of the Florida Platform during lower sea-level stands. The Avon Park Formation, a thick sequence of marine limestone and dolostone, overlies the Oldsmar Formation and is characterized by alternating layers of soft to well-indurated, fossiliferous, tan to light-brown limestone

Data CollectionThe hydrology of Polk County was described by using

existing data and new geologic, water-level, and water-quality data. Data were obtained from published reports and from Federal, State, and County agencies. A network of monitoring wells was established for the collection of water levels and ground-water samples from the surficial, intermediate, and Floridan aquifer systems. Data-collection sites were invento-ried based on a review of existing wells and available water-level and water-quality data in the study area. The locations of wells and springs used for the collection of water-level and water-quality data are shown in figures 9 and 10, respectively. Well construction information is presented in appendix 1.

Geologic and geophysical information from more than 300 wells was used to construct hydrogeologic maps and cross sections of the surficial aquifer system, the intermediate aquifer system/intermediate confining unit, and the Floridan aquifer system in Polk County. This information was obtained from the files of the USGS, FGS, SWFWMD, SFWMD, and from published reports. The data that were analyzed include borehole geophysical logs and lithologic descriptions of well cuttings by geologists and drillers.

Three surficial aquifer system monitor wells were constructed in areas where data were not available. These wells were installed near existing wells that tap the Upper Floridan aquifer to provide a comparison of water levels and water quality between the two aquifers. Split-spoon samples were collected every 5 ft and were used to provide additional data on surficial aquifer system lithology. The altitude of the measuring points of monitoring wells was determined by instrument leveling.

Water samples collected by the USGS and State agen-cies from 130 wells between 1998 and 2003 were used to characterize ground-water quality in Polk County (fig. 10). Water-quality samples from 53 wells and 1 spring in Polk and adjacent counties were collected specifically for this project by the USGS and analyzed for common inorganic constituents and nutrients, mostly in 2003. Sampled wells include public supply, domestic, irrigation, and dedicated monitoring wells.

Geologic FrameworkThe study area is underlain by a thick sequence of

sedimentary rocks that has a minimum thickness of about 5,300 ft, as shown by a deep oil test well at Mulberry (Davis and Associates, 1981). These sediments are predominantly of

CHAPTER 1—Ground-Water Resources of Polk County

1�


and brown, crystalline dolostone. The Avon Park Formation typically is highly fractured and cavernous. Inclusions of gypsum and anhydrite nodules also occur within the lower part of the Avon Park Formation (Navoy, 1986). The formation is distinguished from overlying formations by the abundance of cone-shaped foraminifera of the genus Dictyoconus. The top of the Avon Park Formation ranges from about 0 ft NGVD 29 in northeastern Polk County to about 700 ft below NGVD 29 in the extreme southwestern part of the county (Arthur and others, 2007).

An erosional unconformity separates the Avon Park Formation from the overlying Ocala Limestone of late Eocene age (Stewart, 1966). The Ocala Limestone can contain two distinct lithologic units. The lower unit consists of a white-to-cream to dark-brown, granular, fossiliferous, well-indurated,

dense, limestone and dolostone. The upper unit is described as a white-to-cream or tan, fossiliferous, generally poorly indurated, pure limestone. The Ocala Limestone is recognized by the disc-shaped foraminifera of the genus Lepidocyclina. The top of the Ocala Limestone ranges from about 75 ft above NGVD 29 in the extreme northwestern part of the county to about 450 ft below NGVD 29 in the extreme southwestern part of the county (Arthur and others, 2007). In the extreme northwestern part of the county, the Ocala Limestone is at or near land surface (Stewart, 1966).

Overlying the Ocala Limestone is the Suwannee Limestone of early Oligocene age. The Suwannee Limestone has under-gone extensive erosion and is absent in much of the northern and extreme eastern part of the county (Arthur and others, 2007). The limestone is white, cream, or tan, fossiliferous,

Figure �. Location of wells with periodic or continuous water-level data (well numbers and information in appendix 1).

POLK COUNTY

LAKE COUNTY

SUM

TER

COUN

TY

HILL

SBOR

OUGH

COU

NTY

PASC

O CO

UNTY


OSCEOLACOUNTY

ORANGE COUNTY

81°15′30′45′82°00′


0 10

5

5 15 KILOMETERS

28°15′

28°00′

27°45′

.

98 7654

2 1

999796959291

898884

83

828180

7877

7675 7473

72717069 6764 63

62 6059 585756

55

5049 464544

43

42414039

383736

34333231

3027

2625242322 2118

17

16 15 1413

1210

266265264263

262261260259

258257

255254253 251 250249248

247246

245244243242

241240239

234233232

230229

228227

226 225224223222

220219

218217216215

212211

210209 208

207205 204203

200199

198 197194193

191190189 186

185 184 183182181 180179177

176173170169 167 166 165

164163162161

160159158

157156155154152 151150148 147146

145144 143142 140139

138137

136135134

133 131130129128 127

124123

122 119118 117115

114

113112111110

108 107103 101100

206

102 106105

47 53

6665

267

196

214

52

St. Cloud well

238237236

99EXPLANATION

WELL LOCATIONAND NUMBER

Lakeland

Bartow

WinterHaven

MountainLake

Avon Park

poorly to well-indurated and variably recrystallized. The limestone can be interbedded with calcilutite (calcareous mud, greater than 50 percent silt or clay-size carbonate particles) and calcarenite (calcareous sand, greater than 50 percent sand-size carbonate particles) units. The top of the Suwannee Limestone ranges from about 75 ft above to about 250 ft below NGVD 29 (Arthur and others, 2007). The Suwannee Limestone generally is distinguished from the overlying Hawthorn Group by the lack of phosphatic sand.

Unconformably overlying the Suwannee Limestone is the Hawthorn Group of late Oligocene to Miocene age. Although originally believed to be Miocene in age, more recently the Hawthorn Group has been interpreted to include late Oligocene-aged sediments as well (Scott and others, 2001). Scott (1988) reclassified the sediments of the Hawthorn

to group status because of its areally extensive and mapable lithologic units. In southern peninsula Florida, the Hawthorn Group includes, in ascending order, the Arcadia and Peace River Formations. The Arcadia Formation may contain up to two named members, in ascending order, the Nocatee and Tampa Members. Where both of these members cannot be identified, the section is referred to as the Arcadia Formation (Scott, 1988). The Arcadia Formation is composed of lime-stone and dolostone containing varying amounts of quartz sand, clay, and phosphate grains. Thin beds of quartz sand and clay are scattered throughout the section and generally are calcareous or dolomitic and phosphatic (Scott, 1988). The top of the Arcadia Formation ranges from about 100 ft above to more than 100 ft below NGVD 29 (Scott, 1988). The unit is absent in the northern part of the study area.

Figure 10. Location of wells and spring where water-quality data were collected from 1998-2003 (well numbers and information in appendix 1).

Geologic Framework 1�

POLK COUNTY

LAKE COUNTY

SUM

TER

COUN

TY

HILL

SBOR

OUGH

COU

NTY

PASC

O CO

UNTY


OSCEOLACOUNTY

ORANGE COUNTY

81°15′30′45′82°00′


0 10

5

5 15 KILOMETERS

28°15′

28°00′

27°45′

St. Cloud well

6

3

5 97

4

2

93 908887

85 83

76 73 6659

5348 4442

3429

2825

21 20

11

98

69

54

39

37

23

19

92

15

79

8986

7772 686151

4340 36 35

312724

22

264261

255

243235230

218

201

183

174

171166

165 162160

155

148 147141140

135

125112 109

190

172

159

130

111101

156

263256

253 252251

244 242234229

224223222 221219

214 207 204202198

195

192 188187184

178

175168164

158157

153

149142

134132

126121

120116113

110 104103

94

65

117

9EXPLANATION

WELL LOCATION AND NUMBERSPRING LOCATION AND NUMBER201


SERIES STRATIGRAPHIC UNITGEOLOGY

AND LITHOLOGY HYDROGEOLOGIC UNIT

Holocene andPleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Undifferentiatedsurficial deposits

SandSurficial aquifer

system

Sand, clay

HawthornGroup

Peace RiverFormation

ArcadiaFormation

Phosphate,clay, sand,limestone,

anddolostone

Inte

rmed

iate

aqu

ifer s

yste

m o

rIn

term

edia

te c

onfin

ing

unit

TampaMember

NocateeMember

Suwannee Limestone

Ocala Limestone

Avon Park Formation

Oldsmar Formation

Cedar Keys Formation

Limestoneand dolostone

Uppe

r Flo

ridan

aqu

ifer

Middleconfining unit

LowerFloridan aquifer

Sub-Floridanconfining unit

Flor

idan

aqu

ifer s

yste

m

Limestone anddolostone with someintervals containing

inclusions of gypsumand anhydrite

Limestone anddolostone with beds

of gypsum andanhydrite

Bone ValleyMember

Middlesemiconfining

unit

Cypr

essh

ead

Form

atio

n

Confining unit

Confining unit

Confining unit

Zone 2

Zone 3

Upper permeablezone

Semi-confining unit

Lower permeablezone

Figure 11. Relation of stratigraphic and hydrogeologic units (modified from Barr, 1992; Tihansky and others, 1996; O’Reilly and others, 2002; Sepúlveda, 2002; and Basso and Hood, 2005).

The lowermost sediments of the Arcadia Formation form the Nocatee Member. The Nocatee Member consists of a complexly interbedded sequence of variably phosphatic quartz sands, clays, and carbonates (Scott, 1988). Previously, this unit was called the “sand and clay unit” of the Tampa Limestone by Wilson (1977). In Polk County, the top of the Nocatee Member ranges from about 0 to more than 200 ft below NGVD 29 (Arthur and others, 2007). The unit is absent in all but the southwestern part of the county.

The Tampa Member of the Arcadia Formation consists predominantly of limestone and subordinate dolostone, sand, and clay. Phosphate concentrations are low, generally less than 3 percent (Scott, 1988). The top of the unit ranges from about 50 ft above to 150 ft below NGVD 29 and is present only in southwestern Polk County (Arthur and others, 2007).

Unconformably overlying the Arcadia Formation is the Peace River Formation. The Peace River Formation is composed of interbedded quartz sand, clay, and carbonates, with variable amounts of phosphate. Siliciclastics, however, are the predominant lithology, comprising more than two-thirds of the formation (Scott, 1988). The Peace River Formation is present throughout most of Polk County. The top of the unit generally ranges from about 125 ft above to 125 ft below NGVD 29 (Arthur and others, 2007).

The unit formerly called the Bone Valley Formation was reclassified by Scott (1988) to member status within the Peace River Formation. The Bone Valley Member is a clastic unit consisting of pebble or gravel-sized phosphate fragments and sand-sized phosphate grains in a matrix of quartz sand and clay (Scott, 1988). The presence of phosphate gravels in the

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Figure 1�. Geologic map of Polk County (from Scott and others, 2001).

Geologic Framework 1�


Bone Valley Member is the most important lithologic factor in the differentiation of this member from the remainder of the Peace River Formation. The unit extends over much of the southwestern part of Polk County, where it attains a maximum thickness of about 50 ft (Scott, 1988). Because of its thickness and high concentration of phosphate, the Bone Valley Member has been extensively mined in Polk County. The top of the unit ranges from more than 120 ft to about 60 ft above NGVD 29 (Arthur and others, 2007).

Overlying the Hawthorn Group are the undifferentiated clastic (surficial) deposits of Pliocene to Holocene age, which includes the Cypresshead Formation. The undifferentiated surficial deposits consist primarily of sands, clayey sands, and clay. These deposits are present throughout most of Polk County, except in the extreme northwestern part of the county and along parts of the upper Peace River, where at a few loca-tions, limestone is exposed at land surface. The quartz sands, which make up the upper part of the unit, are fine-to-coarse grained and reach their maximum thickness under the Lake Wales Ridge.

Karst Features

The soluble limestones and dolostones that underlie Polk County have been sculptured by dissolution and weathering processes to form what is known as karst terrain. Characteristic features of karst terrains that are directly related to carbonate dissolution and ground-water flow include sink-holes, springs, caves, disappearing streams, internally drained basins, and subsurface drainage networks. Water percolating through the upper soil zone combines with carbon dioxide, forming a slightly acidic solution. This water passes through insoluble sediments until it reaches the underlying carbonates. These carbonate rocks may be fractured, jointed, and have many voids and cavities that provide conduits for water flow. The voids or fractures can range in size from small vugs to large caverns. Acidic water passing through these openings slowly dissolves the carbonate rocks, and, over a long period of time, results in the formation of enlarged conduits and cavi-ties. As the solution caverns become larger, in some instances, the roofs may not be able to support the overlying sediment. Collapse of the cavity roofs is evident today as sinkholes and sinkhole depressions.

Sinkholes most commonly develop in areas where ground-water recharge rates are rapid and where the overlying siliciclastic sediments are relatively thin or very permeable. Although sinkholes in all stages of development are common throughout Polk County, most occur along the ridges and range from small depressions to large lakes (fig. 13). These sinkholes, which often are filled with permeable surficial sands, provide more direct avenues for water from the surficial aquifer system to recharge the underlying Upper Floridan aquifer. The locations of sinkholes and depressions in Polk County are shown in figure 14. The features presented, which range from about 10 ft to several hundred feet in diameter,

were delineated from USGS topographic maps. Also included may be some man-made features, which can be indistinguish-able from the natural features on the topographic maps. Many of the natural lakes, ponds, and topographic depressions in the county were formed by sinkholes. Larger lakes often were formed by the coalescence of several sinkholes. Continuous high-resolution seismic-reflection surveys of lakes on the Lake Wales Ridge indicate that many of these lakes likely were formed by subsidence activity (Lee and others, 1991; Sacks and others, 1992; Evans and others, 1994; Tihansky and others, 1996).

The existence of karstic features along the upper Peace River and adjacent floodplains between Bartow and Fort Meade (fig. 1) provide a direct hydraulic connection between the river and aquifers at some locations (Lewelling and others, 1998). The Peace River in this area is characterized by shal-low, sometimes exposed carbonate units, with karst features that vary in type and size and include sinkholes, subsidence depressions, dissolution pipes, and enlarged fractures. Patton (1981) and Patton and Klein (1989) mapped more than 90 sinkholes in the upper Peace River floodplain. Along this stretch of the river, the water level in the river often is higher than water levels in the underlying aquifers. The downward head gradient allows the Peace River to lose water to the ground-water system through sinkholes and conduits (fig. 15).

Ground-Water ResourcesThe hydrogeologic system in the study area consists of

a series of clastic deposits underlain by a thick sequence of carbonate rocks. The stratigraphic units underlying the county form a layered sequence of aquifers and confining units. Each aquifer system has unique hydraulic characteristics that determine its potential for water supply.

The uppermost water-bearing unit is the surficial aquifer system. This aquifer system is underlain by and separated from the Floridan aquifer system by the intermediate confining unit or the intermediate aquifer system, both of which restrict the movement of water between the overlying and underlying aquifers. The lowermost hydrogeologic unit underlying the county is the Floridan aquifer system (fig. 11). The Floridan aquifer system has two major water-bearing zones (Upper Floridan aquifer and Lower Floridan aquifer), which are sepa-rated by a less-permeable middle semiconfining unit and/or a middle confining unit. Underlying the Floridan aquifer system are low-permeability limestone and dolostone that contain considerable gypsum and anhydrite, and define the base of the Floridan aquifer system. Generalized hydrogeologic sections (locations shown in fig. 16), based on geophysical and geologic logs, are shown in figures 17 and 18. The sections show the relative positions of the surficial, intermediate, and Floridan aquifer systems. Stratigraphic units, general lithol-ogy, and corresponding hydrogeologic units underlying Polk County are given in figure 11.

Surficial Aquifer System

The surficial aquifer system is unconfined and consists of unconsolidated clastic deposits that range in age from Pliocene to Holocene. The unit is composed primarily of fine- to medium-grained quartz sand near land surface that grades with depth to silty and clayey sands. The lithology and texture of the sediments within the surficial aquifer system can vary considerably both vertically and laterally. The base of the surficial aquifer system is defined by the first persistent beds of Miocene or Pliocene age sediments containing a substantial increase in clay or silt.

Thickness of the surficial aquifer system in Polk County is variable. A generalized contour map of the thickness of the surficial aquifer system is shown in figure 19. The thicknesses shown in figures 17 to 19 represent the thickness of both saturated and unsaturated undifferentiated sediments. In much of the western one-third of the county, thicknesses gener-ally are less than 50 ft. In the Green Swamp area where the Upper Floridan aquifer is near land surface, deposits from the surficial aquifer system may be only a few feet thick or less. Along parts of the Peace River south of Bartow, the surficial aquifer system exists as thin sand units within the streambed and exposed cut banks that may be several feet or less in

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Figure 1�. Sinkhole-formed lakes near Winter Haven, Florida (source: Land Voyage 15-meter satellite).

Ground-Water Resources 1�

�0 Hydrology of Polk County, Florida

thickness (Lewelling and others, 1998). The surficial aquifer system generally thickens toward the east, especially along the southern part of the Lake Wales Ridge where the thickness can exceed 200 ft.

The surficial aquifer system is recharged primarily by the infiltration of rainfall. Much of the rain that falls in the study area, however, drains into streams or lakes or is lost to evapotranspiration. The remaining rainfall percolates into the unsaturated surficial deposits and recharges the surficial aquifer system. In extreme eastern Polk County, the surficial aquifer system also is recharged by the upward leakage of water from the Upper Floridan aquifer where heads in the underlying Upper Floridan aquifer are higher than in the surfi-cial aquifer system. Other sources of recharge include the land application of wastewater and reclaimed water, septic-tank

effluent, irrigation of agricultural land or residential areas, and lateral ground-water inflow from adjacent areas. Water is discharged from the surficial aquifer system by evapo-transpiration; by seepage into lakes, wetlands, and streams; by downward leakage to the Floridan aquifer system in areas where the potentiometric surface of the Upper Floridan aquifer is below the water table; and by pumpage.

Even though most water in the surficial aquifer system flows vertically to recharge the Upper Floridan aquifer, there is also a lateral component of flow. The lateral direction in which the water flows in the surficial aquifer generally is governed by the topography. Water in the surficial aquifer system usually flows laterally from areas of higher altitude and discharges into lakes, streams, and wetlands in areas of lower altitude. The altitude of the water table varies from one

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EXPLANATIONSINKHOLE OR DEPRESSIONFEATURE -- Features were

delineated from 1:24,000U.S. Geological Surveytopographic maps

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Figure 1�. Location of sinkholes and depressions in Polk County.

physiographic region to another. In low, flat, poorly drained areas, such as in the Green Swamp area in northern Polk County, the water table generally is at or near land surface throughout most of the year. The stage of the streams and lakes also represents the altitude of the water table. In areas of relatively high land-surface altitude, the water table generally is a subdued reflection of

Documents

Hydrology of Polk County, Florida - USGS · Hydrology of Polk County, Florida By Rick M. Spechler and Sharon E. Kroening Prepared in cooperation with the Polk County Board of County